The present invention relates to an inertia drive type starter motor for an internal combustion engine.
Inertia drive type starter motors rely on inertia of the pinion or clutch mechanism to move the pinion from a rest position to an engaged position against a spring force when the motor is switched on. Such motor drives have been used successfully but do suffer from false starts whereby the pinion is disengaged prematurely by sudden rotation of the engine being started which occurs not only when the motor starts but also when the engine misfires or fires but does not start. These false starts disengage the starter motor pinion requiring the starting sequence to be re-initiated. They can also suffer from bounce out or pump out which is a condition where the pinion oscillates along the shaft while engaging the engine ring gear and is a condition that can result in complete disengagement.
Thus a positive engagement mechanism for an inertia drive is desirable. Two such type drives are shown in U.S. Pat. Nos. 2,923,162 and 4,502,429. U.S. Pat. No. 4,502,429 shows a device which is very complex while U.S. Pat. No. 2,923,162 shows a device wherein the inertia drive is not assisted by the holding mechanism.